An article by Robert E. Brooks entitled "Micromechanical Light Modulators On Silicon" in Optical Engineering, Jan./Feb. 1985, pp. 101-106 describes some of the history of the development of display and signal processing systems using minute, reflective, individually deflectable elements. From the earlier use of deformable membranes to generate television images, the technology has advanced to integrated circuit fabrication techniques in which very small cantilevered elements extend above an etched well, for use in digital data processing applications. The state of development in this technology is evidenced by an article by K. E. Petersen entitled "Micromechanical Light Modulator Array Fabricated On Silicon", Applied Physics Letters 31, No. 8, pp. 521-523 (1977), and also in U.S. Pat. No. 4,229,732 issued Oct. 20, 1980 to Petersen and Hartstein. The geometry of the beams or paddles is precisely defined by a pattern of etchable and non-etchable materials used in integrated circuit fabrication, and the circuit structure may also include semiconductor control circuitry and devices.
The cantilevered element is typically a silicon beam or paddle having a very thin reflective metallic coating. An electrostatic charge on the cantilevered element relative to the well determines the extent of deflection of the element. This type of device is advantageous because very small micromechanical modulators (e.g. 60 microns on a side) can be fabricated with close center-to-center spacings (e.g. 87.5 microns). Thus they can be distributed in small arrays of desired resolution and overall size. The individual elements are compatible with the sizes of other elements, such as sensor arrays, that may be fabricated by modern integrated circuit techniques.
When illuminated with a flood beam of light, the micromechanical modulator array provides a means of high speed parallel transmission of a great amount of data. While the first uses of such modulator arrays were for generating TV displays, attention was thereafter directed to other functions, such as generating Fourier transforms. More recently, the parallel processing implications have been considered at length relative to optical interconnection, with data or without transformation, of microelectronic circuits. A summary of thinking in this respect has been provided by J. W. Goodman et al in "Optical Interconnections For VLSI Systems", Proceedings of the IEEE, Volume 72, No. 7 (July 1984), p. 850 et seq. This article mentions some of the practical considerations involved in implementation of these systems, as does the above-referenced article by Brooks. Further, the Brooks article also discusses possibilities for usage of micromechanical light modulators for optical plane readout, image subtraction, nonlinear image processing and matrix arithmetic. In some of such systems, and also in recently issued U.S. Pat. No. 4,569,033 to Collins et al, entitled "Optical Matrix-Matrix Multiplier Based On Outer Product Decomposition", manipulation of parallel signals in the course of transmission is shown to be conceptually feasible. However, providing practical systems that have a desired bandwidth, low power drain, signal-to-noise ratio, and intercommunication capability at reasonable cost presents many problems that have heretofore not been confronted in detail. An example is the application of this technology to the generation of output signals from low noise sensor arrays. Such arrays must be cryogenically cooled and thermally isolated. Thus it is not desirable to couple a large number of leads into the low temperature zone because of heat losses through the wires. Also, in order to minimize energy requirements, the available volume about the sensor array is usually very limited, and this substantially complicates the problems of obtaining adequate level output signals.